Na+-independent transport of bipolar and cationic amino acids
across the luminal membrane of the small intestine.
Gyldenlve, Bjarne, Munck & Lars Kristian Munck.
Department of Medical Physiology, The Panum Institute, University
of Copenhagen, DENMARK
APStracts 3:0403R, 1996.
Measuring unidirectional influx across the brush border membrane of
intact rat jejunal and rabbit ileal epithelia the role of sodium in
transport of bipolar and cationic amino acid and their interactions
were examined in vitro. The chloride-dependent and [beta]-alanine
inhibitable B0,+ present in rabbit ileum was blocked by combining
inhibition by [beta]-alanine with Na+- or Cl--free conditions. Under
these conditions lysine influx across the brush border membrane is
Na+-independent. All Na+-independent influx of cationic and bipolar
amino acids is by a system b0,+ equivalent in the brush border
membrane of both species, where a system y+ is not present. System
b0,+ is shown to be a potent exchanger of intracellular leucine for
extracellular lysine and of intracellular lysine for extracellular
leucine. The model used to explain leucine stimulation of mucosa to
serosa lysine transport can explain Na+-dependence of net lysine
absorption. Assuming that b0,+ in situ, like in the Xenopus Laevi
oocyte, acts as an obligatory exchanger, this model can also explain
the effects of lysine on short circuit current and net transport of
sodium, and the effect on transport capacity by preincubation at
sodiumfree conditions.
Received 3 July 1996; accepted in final form 25 October 1996.
APS Manuscript Number R385-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996